Impact of UV radiation of different wavebands on pigments and assimilation of 15N-ammonium and 15N-nitrate by natural phytoplankton and ice algae in antarctica

Abstract

The effects of UV radiation of different wavebands on pigments and assimilation of 15 N-ammonium and 15 N -nitrate of natural phytoplankton and sea-ice algae were studied during the «Polarstern« cruise (ANT X/7) in the Weddell Sea, Antarctica (December 3, 1992 to January 22, 1993). UV radiation experiments were performed with special Philips lamps (TL 20W/12) in connection with cut-off filters (WG 295, WG 305 and WG 320) under controlled laboratory conditions at +2°C. Chlorophyll a biosynthesis was more affected by UV-B radiation than chlorophyll c. Uptake of 15 N-ammonium and 15 N-nitrate by ice-algae was less reduced by UV-B than that of the phytoplankton samples. The inhibitory effect was dependent on the applied UV fluence rate and the species composition of the assemblages. Patterns of 15 N-labelled free amino acids and the pools varied in dependence on the wavebands of UV irradiance and the species composition as well. Results were discussed with reference to the different UV targets and the key enzymes of nitrogen metabolism.